The present invention relates to a gun tube provided with rifling for producing a rifling force which becomes active when a projectile is fired from the gun tube.
The service life of such rifled gun barrels is known to depend significantly on the rifling force. This relationship, along with the design of a profile composed of grooves and lands and a corresponding development of spin in the gun tube, is explained and described in detail in HANDBOOK ON WEAPONRY, published by Rheinmetall GmbH, 2nd English Edition, 1982, pages 572 to 579. Accordingly, the rifling force R(x) along the path of the projectile x in the longitudinal direction of the gun tube can be described, in a good approximation, as follows: ##EQU1## under the condition that: ##EQU2## where J is the moment of inertia of the projectile about its longitudinal axis;
D is the caliber of the gun tube; PA1 m.sub.G is the mass of the projectile; PA1 y is the developed circumferential direction; PA1 p(x) is the gas pressure acting ont he projectile base; PA1 v.sub.G (x) is the velocity of the projectile; PA1 .alpha.(x) is the rifling angle.
This makes it clear that with a given projectile mass m.sub.G, projectile velocity v.sub.G (x) and gas pressure curve p(x), the character of the rifling of the gun barrel under consideration decisively influences the rifling force curve R(x).
However, it is a disadvantageous fact that in the constant twist design which has been employed most frequently for manufacturing technology reasons, particularly in large caliber gun tubes, in which the rifling angle .alpha.(x) is independent of the projectile path x, the rifling force curve R(x) is proportional to the gas pressure curve p(x). A distinct, local maximum of the rifling force occurs which coincides in its location in the gun barrel with the gas pressure maximum and leads to undesirably high, local stresses.
Some time ago, calculations were made in an attempt to reduce the rifling force by employing a parabolic, sinusoidal or cubic-parabolic rifling, as described in the above mentioned HANDBOOK ON WEAPONRY. These types of rifling, particularly those identified as progressive in FIG. 1137 at page 575 the HANDBOOK ON WEAPONRY, show that with parabolic and cubic-parabolic rifling, a high rifling force R(x) occurs at the muzzle end of the gun tube and may adversely influence the trajectory of the projectile. Moreover, it has a torsional impulse effect on the gun tube and thus generates undesirable vibrations of the gun tube about its bore axis, putting additional stress on the projectile.
As can also be seen in the above mentioned FIG. 1137 of the HANDBOOK ON WEAPONRY, the sinusoidal rifling still shows a distinct maximum of rifling force but also a clearly reduced rifling force at the muzzle end of the gun tube. Since, however, in the prior art gun tubes provided with cubic parabolic rifling for automatic cannons, the rifling angle .alpha.(x) increases from an initial rifling angle .alpha..sub.A =0.degree. to a final rifling angle .alpha..sub.E =6.5.degree. at the gun tube muzzle, the advantage realized by the lower rifling force at the muzzle is in part consumed by the distinct reshaping of the rotating band of the projectile. These relationships become less favorable, the broader the rotating band.
For artillery tubes whose projectiles customarily have particularly wide rotating bands, a progressive rifling angle curve beginning with an initial twist .alpha..sub.A =0.degree. increases the stress on the rotating bands, particularly if the customary final rifling angle of .alpha..sub.E .apprxeq.9.degree. is to be realized. In this case, almost the entire width of the rotating band is reshaped by the change in rifling angle so that the danger exists that the rotating band might fail in the gun tube.